The present invention relates to a traction modifying differential, and more particularly, to such a differential of the type in which the differential gearing may be locked in response to an electrical input signal.
Traction modifying differentials of the type to which the present invention relates typically include a gear case defining a gear chamber, and disposed therein, a differential gear set including at least one input pinion gear, and a pair of output side gears. A clutch pack is typically disposed between at least one of the side gears and an adjacent surface of the gear case, such that the clutch pack is operable to limit relative rotation between the gear case and the one side gear. In most differentials of the type described, engaging the clutch pack is achieved by one of several different approaches.
In one approach, a "locking differential" of the type illustrated and described in U.S. Pat. No. Re 28,004, assigned to the assignee of the present invention and incorporated herein by reference, the clutch pack is normally disengaged. When one of the wheels begins to spin out, relative to the other wheel, a speed sensitive mechanism senses the speed differential and, by means of a ramping mechanism, locks the clutch pack solid. Thereafter, both outputs of the differential rotate at the same speed.
U.S. Pat. No. 5,019,021, also assigned to the assignee of the present invention and incorporated herein by reference, illustrates another approach, a "limited slip differential" in which the loading on the clutch pack may be varied in response to an external electrical input signal, thus varying the amount of slip within the clutch pack, and therefore, the amount of bias torque transmitted from one side gear to another. As is well known to those skilled in the art, in a limited slip differential, there is typically a certain amount of "slip", or speed differential, between the two side gears whenever the vehicle encounters less than optimum traction conditions.
Although the performance of limited slip and locking differentials of the type shown in the above-incorporated patents is, in general, quite satisfactory, there are certain disadvantages of the particular design, for certain vehicle applications. The requirement for at least one, and typically two clutch packs, adds substantially to the overall cost of the differential, especially when the individual clutch disks are provided with a relatively more sophisticated friction material, able to withstand elevated temperatures under continuous slipping conditions.
In addition, there are many vehicle applications in which it would be desirable to provide a traction modifying differential, to replace an existing open differential, but wherein the traction modifying differential would have to fit within the same space currently occupied by the open differential, in order to avoid a complete redesign of the surrounding structure. In such a situation, the addition of one or two clutch packs, within an existing differential case, would be impossible without redesigning the pinion gears and side gears and downsizing them, which is typically not feasible.